Detergent compositions designed for use in cleaning, particularly automatic dishwashing and laundry methods are well known, and a consistent effort has been made by detergent manufact urers to improve the cleaning and/or rinsing efficiency of said compositions as reflected by numerous patent publications.
The general problem of the formation of deposits as spots and films on the articles in the wash, and on the dishwasher and washing machine parts is well known in the art.
Whilst the general problem of deposit formation is known, a full understanding of the many facets of the problem is however still an active area of research.
A range of deposit types can be encountered. The redeposition of soils or the breakdown products thereof, which have previously been removed from the soiled tableware in the washload, provides one deposit type. Insoluble salts such as calcium carbonate, calcium fatty acid salts (lime soaps), or certain silicate salts are other common deposit types. Composite deposit types are also common. Indeed, once an initial minor deposit forms it can act as a "seeding centre" for the build up of a larger, possibly composite, deposit structure.
Deposit formation can occur on a range of commonly encountered substrate surfaces including a range of fabric types, plastic, glass, metal and china surfaces. Certain deposit types however, show a greater propensity to deposit on certain substrates. For example, lime soap deposit formation tends to be a particular problem on plastic substrates, and silicate deposit formation tends to occur on glassware.
The formation of insoluble carbonate, especially calcium carbonate, deposits is a particular problem. There is a general appreciation in the art, as represented for example by EP-A-364,067 in the name of Clorox, CH-A-673,033 in the name of Cosmina, and EP-A-551,670 in the name of Unilever, that calcium carbonate deposit formation is a particular problem when non-phosphate containing detergent formulations are employed. In general, this can be explained by the slightly inferior builder capacity of the typically employed non-phosphate builder systems in comparison to phosphate builder formulations. The problem of calcium carbonate deposit formation is understood to be especially apparent when these formulations contain a carbonate builder component, as for example is essential to the compositions taught by EP-A-364,067.
The Applicants have now found that the problem of CaCO.sub.3 deposit formation can exist even in the absence of a carbonate builder component in the machine dishwashing and laundry detergent formulations, and especially when that formulation contains no phosphate builder component. The naturally sourced, inlet water to washing machines can be a sufficient source of Ca.sup.2+ and Mg.sup.2+ ions and HCO.sub.3- /CO.sub.3.sup.2- ions to make deposit formation a problem. Whilst the salt softening system, through which the inlet water will pass prior to entry into the main cavity of the dishwasher machine, can be efficient at removing the naturally present Ca.sup.2+ and Mg.sup.2+ ions it is inefficient at removing the HCO.sub.3- /CO.sub.3.sup.2- ions which therefore enter into the wash/rinse solution.
The Applicants have now established that both the levels of Ca.sup.2+ /Mg.sup.2+ hardness ions and the levels of HCO.sub.3- /CO.sub.3.sup.2- ions in the wash/rinse water of the dishwasher machine are factors controlling calcium carbonate deposit formation. Critical levels of both components must be exceeded for carbonate-related deposit formation to occur. These critical levels are to an extent interdependent. Thus, even in wash solutions containing high levels of one component deposit formation will not occur in the absence of the critical level of the other component.
A relatively high level of Ca.sup.2+ ions in the wash solution can be desirable for the effective performance of certain enzyme components of the detergent formulation, particularly lipolytic and proteolytic enzymes. Such higher levels of Ca.sup.2+ tend to be present when non-phosphate built formulations are employed. Whilst these relatively high levels of Ca.sup.2+ are desirable for enzyme performance, calcium carbonate deposition will tend to occur if the solution contains a level of carbonate ion above the critical limit for deposit formation.
The Applicants have also established that the formation of deposit "seeding centres", which in turn enable the build up of more substantial deposits, occurs most commonly in the rinse cycle of the dishwasher machine. Deposit build up is most apparent on the heater element of the dishwasher machine. It has also been established that the problem is most apparent when more alkaline formulations, such as those of pH of 9.8 and above, are employed. An upper limit to the pH of about 11.5 has been found to be preferred for the effective working of other preferred components of the composition such as peroxyacid bleaches and enzymes.
The Applicants have found that the problem of calcium carbonate deposit formation may be effectively ameliorated by the inclusion of an amino tricarboxylic acid (ATCA) component in combination with an acrylic acid containing polymer having a molecular weight of less than 15,000 into the detergent formulation.
In an automatic dishwashing context, it has been found that acrylic acid containing organic polymers of higher molecular weight, such as the commonly used maleic/acrylic acid copolymers of molecular weight from typically 40,000 to 80,000, did not provide equivalent deposit formation prevention capability. Indeed, the formation of the insoluble calcium salts of such higher molecular weight polymers was noted in certain circumstances potentially to lead to a worsening of the deposition profile of the compositions in use.
When the combination of said amino carboxylic acid and polymer components is employed in a non-phosphate built formulation the occurrence of calcium carbonate deposits is essentially comparable to that obtained for a more highly built, phosphate containing formulation which does not contain these components.
The Applicants have also found that carboxylates and polycarboxylates, particularly citrates, are especially useful components of the compositions of the invention because of their magnesium binding capacity which tends to prevent the formation of insoluble magnesium salts, such as magnesium silicate on the articles in the wash. Such polycarboxylates also provide calcium binding capacity to the compositions, thus contributing further to the prevention of the formation of calcium salt deposits.
The Applicants have also found that the more effective control of calcium carbonate deposition can also lead to benefits in the prevention of the formation of other deposit types, particularly lime soap deposits and silicate deposits.
Lime soap deposits are most commonly encountered when the washload contains fatty soils, which naturally contain levels of free fatty acids, and when lipolytic enzymes are components of the formulation. Lipolytic enzymes catalyse the degradation of fatty soils into free fatty acids and glycerol. Silicate is a common component of machine dishwashing formulations, where it is added for its china and glass care capability. It is the Applicant's finding that by preventing the formation of calcium carbonate deposit "seeding centres", most particularly in the rinse cycle, the build up of other deposit types from these "seeding centres" is also prevented.